1. Field of the Invention
The present invention relates to apparatus for making physical interconnections of, for example, wire, coax, fiber, etc. in places such as telephone communication systems. More particularly, it relates to distributing frames used in telephone communication systems for efficiently providing electrical connections between various telephone circuits, and to a method for determining connection density in such apparatus, so as to efficiently aid in their design.
2. Background Art
It is believed that the earliest patent for a telephone distributing apparatus is U.S. Pat. No. 816,847, issued to Frank B. Cook, in 1906. It was followed by U.S. Pat. No. 822,590, issued to Franz J. Dommerque, shortly thereafter, also in 1906.
Conventional Distributing Frames (DF's) used in telephone systems are essentially a crosshatch of vertical and horizontal planes, so that outside cable facilities terminated on the vertical side may be interconnected to central office equipment facilities, terminated on the horizontal side. Interconnection of outside terminals and inside terminals is accomplished by means of a connection known as a cross-connection, or jumper. This usually is a two-wire cord, but may also be optic fiber, coax, or any material suitable for conducting telecommunications transmissions. Vertical planes provide a means for cross-connections to move vertically, and horizontal planes, or shelves, provide a means for cross-connections to move horizontally.
Such distributing frames have known limitations. A better approach is outlined in U.S. Pat. Nos. 5,459,644 and 5,704,115, issued to the present inventor, the entire disclosures of which are hereby incorporated by reference. These patents disclose a readily expandable structure. However, because of the large base of more conventional installations, the structures disclosed in these patents are often not utilized. There is a long felt need for a technique to expand conventional distributing frame structure, and for structures along more conventional lines that can be expanded to provide for an ever increasing number of required interconnections.
FIGS. 1A, 1B and 1C illustrate the framework of a common conventional two-sided linear distributing frame design, consisting of fifty verticals 1 (V1-V50) and 12 shelves 2 (S1-S12). A common standard for shelf and vertical spacing is 8 inches (20.3 cm), and the width of shelves and verticals is about 2 feet (70 cm). Rings 3 (R1-R12) are located at the intersections of shelves and verticals to facilitate and control the passage of cross-connections from vertical to horizontal planes. Conventionally, DF's expanded along the line of the DF in the horizontal direction, as shown by the Growth Arrow G in FIG. 1A. This results in increasing the number of verticals and the length of the shelves, while the number of shelves and height of verticals remain constant.
In FIGS. 2A and 2B, connector blocks 4 (VB1-VB12) are mounted on the outside edge of the vertical 1 (V1). Attached to the connector 4 (VB1) is a connector tail 5, which travels on one face (called the cable face—shown as the back face in FIG. 2A) of the vertical 1, through a slot 6, and down into the cable vault or subfloor splicing trap (not shown), where it is spliced into the outside network. A conductor path exists from the connector tail 5, through the block 4, to terminals projecting from the block 4. Presently used 310 type connectors have a termination capacity of 100 pairs, and twelve are typically mounted on a vertical 1, making the total termination capacity of the vertical 1 1,200 pairs. On the horizontal side of the frame, central office equipment terminal blocks 7 (HB1-HB7) are mounted on the edge of the shelf 2. The terminals on this block likewise project through the block, where they are connected to a central office equipment cable 8. This cable travels on the lower face of the shelf 2, and up the cable face of the vertical 1, to an overhead cable rack 9, leading to the central office equipment (C.O.E—switch or other equipment. The termination capacity of the equipment terminal blocks on the horizontal side is approximately the same per linear foot as on the vertical side. On a working DF, the vast majority of verticals 1 are equipped with connector blocks 4 on the vertical side that are connected to the outside cable network. Similarly, on the horizontal side of a working DF, and the vast majority of shelves 2 are equipped with terminal blocks 7 that are connected to equipment cable, leading to the switch or other central office equipment.
FIGS. 3A, 3B and 3C illustrate a DF that has expanded to 100 verticals 1 and is fully equipped with both vertical connector blocks 4 and horizontal terminal blocks 7. A single cross-connection 10 runs from vertical block VB7 on vertical V1, along the front face (as shown in FIG. 3C), called the cross-connect face, of the vertical plane of the vertical V1, through the ring 3, onto shelf S12, and across shelf S12 to horizontal equipment block HB5. The path that has been taken for this connection is defined as a ‘correct’ path: i.e., starting at the VB on the vertical, the cross-connection travels on the cross-connect face to the ring at the shelf level of the HB, through the ring at that level, onto the shelf and continues on that shelf to the HB where it terminates. This connection could have been run as follows: VB7 on V1→R4 on V1→along S4 (because its level is more convenient for installation)→R4 on V5→up the cross-connect face of V5→R12 on V5→across S12 to HB5. Incorrect routing of cross-connections in this manner causes an overload of cross-connections on the middle level shelves and an underutilization of the lower and upper shelves.
A single short cross-connection is shown in FIGS. 3A, 3B and 3B to illustrate the complete path using correct routing that a single connection may take. It is obvious, since the vertical height never increases due to DF expansion, that the vertical portion of any cross-connection is always limited to the height of the vertical. However, the horizontal portion of any cross-connection is limited only by the length of the shelf, which is initially much greater than the height, and the potential for much longer connections increases as the shelves grow longer due to DF expansion.
Longer connections cause larger piles of connections to occur on the shelves of a DF. Historically, much effort was expended to limit the horizontal length of cross-connections on conventional linear DF's. However, as a DF expands and frame activity (connects and disconnects) increases, random intermingling becomes difficult to control. This causes longer connections (on the average) to occur, thus causing bigger piles of connections. Misrouting of new connections and non-removal of dead connections only compound the problem.
To illustrate the effects that multiple connections have on connection densities on a DF, we must first define the places where cross-connection densities will be measured. The area between adjacent shelves on the cross-connect face of a vertical is defined as a vertical cross-section, and the area between adjacent verticals on the upper face of a shelf is defined as a horizontal cross-section. Vertical cross-sections take the number of the shelf of the lower shelf boundary; horizontal cross-section numbers take the number of the vertical of the lower vertical boundary. FIGS. 4A and 4B illustrates a typical vertical 1 and a portion of a typical shelf 2. Vertical cross-section numbers 11 are shown on the vertical 1 in FIG. 4A, and horizontal cross-section numbers 12 have been shown on the shelf 2 in FIG. 4B.
FIGS. 5A and 5B illustrates the effects of a small number of cross-connections on the densities in the cross-sections 11 on a vertical plane 1 and the cross-sections 12 of a horizontal plane 2. In FIG. 5A, 5 cross-connections 10 emanate from 4 vertical blocks 4, and travel across the cross-connect face of the vertical 1, and arrive at 3 rings 3, where they disperse onto their respective shelves 2. The vertical densities caused by these connections are shown as the count 13 of the cross-connections passing through each vertical cross-section 11. Note that the direct connection, VB7 to R7, does not contribute to the vertical density count 13 of any vertical cross-section 11, since it does not travel through any vertical cross-section 11. In FIG. 5B, 5 cross-connections (not the same 5 cross-connections as in FIG. 5A) enter the shelf 2, and disperse to the various HB's 7 on the edge of the shelf 2. Horizontal densities caused by these connections are shown as the count 14 of the cross-connections passing through each horizontal cross-section 10.
Cross-connection lengths can be accurately measured by counting the number of cross-sections (11 & 12) traversed by a cross-connection and neglecting the widths of the vertical and horizontal planes (1 & 2). Thus, a direct cross-connection, such as VB7 to R7 in FIG. 5A, has zero length, since it does not traverse any cross-sections. Average cross-connection length can then be calculated by summing the densities in all the cross-sections, and dividing by the total number of connections. The average vertical component can be calculated by adding the vertical densities and dividing by the number of connections, and the average horizontal component can be calculated by adding the horizontal densities and dividing by the number of connections. For the cross-connections shown in FIG. 5A,Average Vertical Length=(0+0+0+1+2+2+3+2+2+2+1)/5=15/5=3
For the cross-connections shown in FIG. 5B,Average Horizontal Length=(2+4+4+2+1+1)/5=14/5=2.8
FIG. 6 illustrates the final state of a vertical 1 when the shelf 2 destination of each cross-connection was perfectly random. At maximum capacity, each connector 4 would have 100 cross-connections 10 emanating from it. Assuming they were evenly dispersed, each ring 3 would have 100 cross-connections 10 passing through them, and onto the shelves 2 (S1-S12). If the dispersal were perfectly random, the number of cross-connections between each VB and each ring 3 would be 100/12=8.33. The resulting densities 13 in each of the vertical cross-sections 11 are shown. For the perfect random dispersal shown, these densities may be calculated using the following relationship:Dv=2kvs(S−s),                where                    kv=Vertical Connection Constant=8.33            s=Vertical Cross-section#=Lower Shelf#            S=Total Number of Shelves=12                        
Note that the maximum density occurs at the midpoint, and that its value is one half of the total number of connections present on the vertical (1200/2). The average vertical connection length for FIG. 6 may also be calculated by summing the densities and dividing by the total number of connections on the vertical:
                              Average          ⁢                                          ⁢          Length                =                ⁢                                                                              (                                      183                    +                    333                    +                    450                    +                    533                    +                    583                    +                                                                                                                                            600                    +                    583                    +                    533                    +                    450                    +                    333                    +                    183                                    )                                                              /          1200                                        =                ⁢                  4764          /          1200                                        =                ⁢        3.97            
Average length may also be calculated using the following formula:
                              Average          ⁢                                          ⁢          Vertical          ⁢                                          ⁢          Length                =                ⁢                                            (                                                S                  2                                -                1                            )                        /            3                    ⁢          S                                        =                ⁢                                            (                                                12                  2                                -                1                            )                        /            3                    ×          12                                        =                ⁢        3.97            
For S>>1, the above relationship can be simplified to S/3, or ⅓ the Vertical Height.
The justification for the assumption of perfect randomness in the vertical direction is based on the following:                1. Since the vertical distance is very small, there is no need to worry about it        2. Therefore, no attempts were made to control vertical randomness        3. Direct observation—all verticals on a DF exhibit the pattern of FIG. 6        
On the horizontal side of a DF, patterns cannot be distinguished due to the numbers of cross-connections present. However, relative pile sizes of cross-connections can be compared. Invariably, the largest pile of connections occurs at the midpoint, and is the starting point for congestion problems, should they occur. Piles of connections at the ends are sparse by comparison.
A fully connected DF at maximum vertical randomness would be one in which all the verticals are completely connected at maximum randomness, as shown in FIG. 6. In this case, 100 Cross-connections would emerge from every ring on every shelf of the DF. If the dispersal from ring to destination HB (on every shelf) is also completely random, then the vertical relationships for density and length can be adapted for use with horizontal side variables. Density and length relationships at maximum horizontal randomness are as follows:DH=2kHv(V−v),                where                    kH=Horizontal Connection Constant=100/V            v=Horizontal Cross-section#=Lower Vertical#            V=Total Number of VerticalsAverage Horizontal Length=(V2−1)/3V=V/3 for V>>1                        
However, a critical distinction between horizontal and vertical relationships exists. The Vertical Connection Constant would change only when the concentration of terminals on the verticals changed, which, in turn would cause different numbers of cross-connections to emerge from each ring, thus changing the Horizontal Connection Constant. In contrast, the Horizontal Connection Constant changes for different size DF's, or as a single DF expands, because the number of destination HB's varies with each size. For example, if there are fifty verticals, then the number of cross-connections between each ring and each HB would be 100/50=2, if the DF has 100 verticals, the number would be 100/100=1, etc. Although the numbers of connections between ring and HB are decreasing, the lengths that the connections are traveling on the shelf are increasing, causing densities to increase significantly. This can be termed the Linear Expansion Problem.
FIGS. 7A and 7B and FIGS. 8A and 8B illustrate a typical shelf 2 undergoing physical expansion. The initial shelf 2 starts at fifty verticals in FIG. 7A, and expands to 100 verticals 1, in FIG. 7B. FIGS. 8A and 8B illustrate, respectively, expansions to 200 and 300 verticals 1. Each shelf 2 in the two figures has 100 cross-connections randomly dispersing from each ring 3. Thus, the 50V shelf contains 5,000 connections, the 100V shelf contains 10,000 connections, the 200V shelf 20,000 connections, and the 300V shelf 30,000 connections. Since it is impossible to draw that number of connections, only the densities 14 for selected cross-sections 12 are represented. Note that the densities 14 are low and stable (196-199) at the ends, but that half of the total connections on each shelf are present at the midpoint of the shelf: 2,500 at V25 on the 50V shelf, 5,000 at V50 on the 100V shelf, 10,000 at V100 on the 200V shelf, and 15,000 at V150 on the 300V shelf.
FIG. 9 is a graph of cross-connection densities for all cross-sections of shelves of various lengths. Curve 15 represents the density distribution for a 100V shelf; curve 16 for a 200V shelf, curve 17 for a 300V shelf, curve 18 for a 400V shelf, and curve 19 for a 500V shelf. The series of 5,000 cross-connection increases in maximum density from each of curves 15, 16, 17, 18, 19 to the next curve, strongly suggests that there is a limit beyond which a conventional linear DF should not be extended when full random connectivity is present.
When considering DF's during physical expansion, the time required for enough random intermingling to occur to cause a new density distribution can vary from DF to DF. When DF activity is volatile—new service demands, new technology introduced, change of service requests, etc., the change can be quite rapid. When DF activity is stable, the change is slow to occur, or may never occur. Software that chooses shortest connections for service requests also slows the randomization process, but at some point, the only choices available to satisfy customer demand may be long connections. The extent to which randomization has occurred on a DF, whether through expansion or increased activity, or both, can be determined through physical inspection.
FIG. 10 graphically compares density distributions for a 500V shelf with 50,000 horizontal cross-connections under varying extents of randomness. If we consider a 500V shelf with barriers at every 100V, such that no cross-connection could physically travel from one 100V group to another, we effectively would have five separate 100V shelves, end to end, each with its own random density distribution. This is represented by curve 22. If we removed the barriers, but only allowed random intermingling up to a 100V span (i.e., each ring is connected only to the closest 100 HB's), then the density distribution would be as shown in curve 23. The flat portion from V100 to V400 on curve 23 is due to the fact that, emerging from each ring, the 100 cross-connections may travel 50V to the right or left to connect to the 100 closest HB's. Note that this results in a substantial (50%) density reduction from the maximum value on curve 22. The bumps at the ends of curve 22 are due to the fact that connections emerging from rings near the ends have no choice but to travel primarily inward to reach the closest 100 HB's, resulting in longer end connections, and larger end densities. Curve 21 represents the density distribution when random intermingling is allowed up to 250 verticals, or one half of the length of the 500V shelf (50% randomness). Note that there is a distinct reduction at the midpoint, as compared to maximums at V125 and V375, but that these maximums are below the maximum for the 200V full random density 16 shown in FIG. 9. Curve 20 represents the full random density distribution over the entire 500 verticals. Densities increase continuously from the ends to the middle, where the maximum value is reached.
Density curves 20, 21, 22, and 23 can be directly related to pile sizes on a DF shelf. The exact number of cross-connections at a specific point on a shelf may be impossible to determine, but a pile of 1,000 is easily distinguished from a pile of 5,000, and 5,000 from 10,000, etc. Further, even without a specific number reference, the pattern of pile sizes can be discerned. If the piles are larger at the ends with a smaller flat portion between them, then the randomness has been controlled, as in curve 23. If there a decrease in density at the midpoint, we'd be close to curve21. If the piles increase continuously in size from the ends to a maximum at the middle, and there is an observable maximum pile at the midpoint, then it is certain that the randomness is 67% or greater.
The problems of misrouted and un-removed dead connections are often cited as the cause for congestion problems on DF shelves. However, misrouted and dead connections will follow the same horizontal dispersal patterns as correctly routed live connections, and therefore contribute to horizontal densities in the same way, except that the wrong shelves may be used. If misrouting were extreme—say that the upper four shelves (S9-S12) and the two lowest shelves (S1-S2) were not used, then six shelves (S3, S4, S5, S6, S7, S8) would have to carry the load of twelve, thus doubling their densities. Dead cross-connections would contribute in equal proportions to both correctly routed and incorrectly routed cross-connections—i.e., half the dead connections would be on S3-S8, and half on S1-S2 & S9-S12. Therefore, if the non-removal rate of dead connections were 10%, the S3-S8 load would increase by a factor of 2.2. This would be sustainable for curves 22 and 23 in FIG. 10, but not for curves 20 and 21.
The fundamental problem with many prior art attempts to reduce congestion problems on DF's has been the underestimation or misunderstanding of randomness and its relationship to the geometry of points being interconnected. Randomness by itself means that the physical location of circuit elements required to satisfy service requests, becomes, over time, unpredictable, and connection paths required to interconnect them become difficult to utilize, find, or establish. In relation to the geometry of points being interconnected, the more randomness is present, the more important is the geometry of the configuration on which physical connections are made. When randomness is extreme, the more elongated the object, the worse it performs in respect to densities and lengths of connections. A long skinny rectangle, which is what a DF resembles from a distance, is one of the worst shapes on which to interconnect points at random. Abstractly, the most efficient object for interconnecting points in three dimensions with a straight line, is a sphere.
The traditional linear design of the DF has not changed in over 100 years, and with present higher density connectors, there is a limit to physical expansion when randomness is present. This limit is probably about 300 verticals. At 300V, all twelve shelves would contain 15,000 cross-connections at the V150 location, and density levels would be above 10,000 from V64 to V236, or about 58% of each shelf. If the DF operated at 90% capacity, at 100% randomness, shelf densities would be above 10,000 from V73 to V227, or 52% of each shelf.